An apparatus to detect the amount and direction of rotary motion for use in a vibration compensation system in an optical camera. An indicator disk is provided around the output shaft of a motor which actuates a compensation lens to compensate for vibrations to the camera. The periphery of the indicator disk is provided with a series of holes. A pair of photodetectors, are arranged on the periphery of the disk so as to detect the holes passing thereunder. The two photodetectors are separated by a distance equal to 3/4 of the distance between two holes. By comparing the pattern of signals emitted by the photodetectors the direction of rotation of the indicator disk can be determined. Further, the pulses in the output of either photodetector can be counted to determine the amount of movement. The actual direction and amount of movement as calculated is provided to a vibration compensation circuit as feedback for use in controlling the compensation lens.